Added tips to installation docs (#2175)

* Added virtual environment tips

Documented the use of `POWERLINE_COMMAND` env variable for improved performance with virtual environments.

* Clarify client versions

Adding details from the GitHub issues to clarify the installation docs.

* Added troubleshooting tip for Python environments

docs/source/installation/osx.rst

@@ -16,9 +16,13 @@ Python package
        brew install python
 
    .. note::
-      In case :file:`powerline.sh` as a client ``socat`` and ``coreutils`` need 
-      to be installed. ``coreutils`` may be installed using ``brew install 
-      coreutils``.
+      There are three variants of the powerline client.  The fastest is
+      written in C and will be compiled if the compiler and libraries are
+      detected during installation.  The second fastest option is
+      :file:`powerline.sh` which requires ``socat`` and ``coreutils``.
+      ``coreutils`` may be installed using ``brew install 
+      coreutils``.  If neither of these are viable, then Powerline will
+      utilize a fallback client written in Python.
 
 2. Install Powerline using one of the following commands:
 

docs/source/troubleshooting.rst

@@ -193,8 +193,12 @@ I am suffering bad lags before displaying shell prompt
 To get rid of these lags there currently are two options:
 
 * Run ``powerline-daemon``. Powerline does not automatically start it for you.
+  See installation instructions for more details.
 * Compile and install ``libzpython`` module that lives in 
   https://bitbucket.org/ZyX_I/zpython. This variant is zsh-specific.
+* If you are a python package manager, be sure to set ``POWERLINE_COMMAND``
+  to your Powerline command.  See installation instructions for details.
+  
 
 Prompt is spoiled after completing files in ksh
 -----------------------------------------------

docs/source/usage/shell-prompts.rst

@@ -5,8 +5,9 @@ Shell prompts
 *************
 
 .. note::
-    Powerline daemon is not run automatically by any of my bindings. It is 
-    advised to add
+    Powerline can operate without a background daemon, but the shell performance
+    can be very slow.  The Powerline daemon improves this performance
+    significantly, but must be started separately. It is advised to add
 
     .. code-block:: bash
 
@@ -142,3 +143,19 @@ following in ``~/.profile``:
 .. warning::
     Busybox has two shells: ``ash`` and ``hush``. Second is known to segfault in 
     busybox 1.22.1 when using :file:`powerline.sh` script.
+    
+Python Virtual Environments (conda, pyenv)
+==========================================
+
+If your system uses virtual environments to manage different Python versions,
+such as pyenv or anaconda, these tools will add a performance delay to every
+shell prompt.  This delay can be bypassed by explicitly specifying your command
+path.
+
+    .. code-block:: bash
+
+        export POWERLINE_COMMAND={path_to_powerline}
+        
+where ``{path_to_powerline}`` is the full filepath for powerline.  If you
+installed Powerline within an environment, you can find this path for pyenv
+with ``pyenv which powerline`` or for conda with ``which powerline``.